MADRID — Real Madrid needs Cristiano Ronaldo to recover his confidence against Barcelona when the two rivals start another "clasico" series Wednesday in the first leg of the Copa del Rey quarterfinals.

Ronaldo has scored only twice in 13 career games against Barcelona, with his last goal coming in April's cup final to give Madrid its lone victory in the last 12 meetings over the Catalan club.

The Portugal forward has been struggling since coming under criticism for squadering a number of scoring opportunities in last month's 3-1 league loss to Barcelona, and has just one goal so far in 2012.

Ronaldo is the league's top scorer with 21 goals but was clearly frustrated Saturday as Madrid struggled to beat Mallorca 2-1 to maintain its five-point advantage over Barcelona.

Meanwhile, Barcelona rival and recent Ballon d'Or winner Lionel Messi continues to propel the Spanish champions, scoring twice in a 4-2 win over Real Betis on Sunday to take his overall goal tally this season to 33 goals — six better than Ronaldo.

"Strikers live off of streaks," Barcelona midfielder Xavi Hernandez said on Monday. "Leo has always been a player who can make a difference, a decisive player. And he's a player who grows in these types of games, which he loves playing."

While Ronaldo is certain to start, coach Jose Mourinho must devise a tactical formation that can stop the 25-time cup champion without suspended defender Alvaro Arbeloa and injured midfielder Sami Khedira. Forward Angel di Maria trained for the first time in weeks on Monday but Pepe did not, which could leave Mourinho with a big hole to fill as the Portugal defender has played a key role in recent clasicos.

"You can't play well every game," Madrid forward Jose Callejon said after netting the winning goal against Mallorca. "It's the little details that make the difference."

Barcelona will be without injured forwards David Villa and Pedro Hernandez and midfielder Seydou Keita at the Bernabeu, where the European champions haven't lost in six matches.

"We'll go there looking to score goals and try to play the best game possible," coach Pep Guardiola said. "We know the rival we're going up against well. We'll try to play the most complete match possible."

The Spanish rivals have split their previous 16 cup series since 1916 with eight victories each.

The winner of this one will play either Valencia or Levante, who play at the Mestalla stadium on Thursday.

The only lower-tier club left in the competition is on the other half of the draw, where third-division club Mirandes travels to Espanyol on Tuesday. Athletic Bilbao, a 23-time cup winner, welcomes Mallorca in the other quarterfinal matchup, with return legs to be played next week.